Method of recycling fracturing fluids using a self-degrading foaming composition

ABSTRACT

A method of fracturing a subterranean zone penetrated by a well bore preparing a foamed fracturing fluid containing a self-degrading foaming composition with a mixture of anionic surfactant and nonionic surfactant, and a composition thereof. The fracturing fluid containing self-degrading foaming composition forms a substantially less stable foam when the foamed fracturing fluid is recovered during reclaim.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 11/399,223 filed Apr. 06, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to method of recycling foamedfracturing fluids used in fracturing subterranean formations in oil andgas wells. More specifically, the invention relates to a self-degradingfoaming composition that enhances the recycling of foamed fracturingfluids due to its defoaming character during reclaim of the fluid.

2. Description of the Related Art

Natural resources such as gas, oil, minerals, and water residing in asubterranean formation can be recovered by drilling wells into theformation. The fluids in the subterranean formation are driven into thewells by, for example, pressure gradients that exist between theformation and the wells, the force of gravity, displacement of thefluids using pumps or the force of another fluid injected into thewells. The production of such fluids is commonly increased byhydraulically fracturing the subterranean formations. That is, a viscousfracturing fluid is pumped into a well to a subterranean formation at arate and a pressure sufficient to form fractures that extend into theformation, providing additional pathways through which the fluids canflow to the wells.

The fracturing fluid is usually a water-based fluid containing a gellingadditive to increase the viscosity of the fluid. The gelling additivethus reduces leakage of liquid from the fractures into the subterraneanformation and improves proppant suspension capability. The gellingadditive is commonly a polymeric material that absorbs water and forms agel as it undergoes hydration.

In certain applications one or more foaming surfactants are added to thefracturing fluid. A gas is mixed with the fracturing fluid to produce afoamed fracturing fluid, thus ensuring that the pressure exerted by thefracturing fluid on the subterranean formation exceeds the fracturegradient (psi/ft.) to create the fracture. The foamed fracturing fluidis injected by foaming the fracturing fluid with nitrogen or carbondioxide. The foaming composition containing one or more surfactantsfacilitates the foaming and stabilization of the foam produced when thegas is mixed with the fracturing fluid.

After a fracturing fluid has been used to form fractures in asubterranean formation, it is usually returned to the surface fordisposal or recycle. When fluid is returned, it is desirable to have afluid that does not foam. Also, it would be desirable to have theability to recycle the fracturing fluid to form additional fractures inthe same subterranean formation or to form fractures in one or moredifferent subterranean formations. Frequently, foamed fracturing fluidsare not suitable for recycling. In the recycling operations it isdesirable to have a fracturing fluid to be without foam for ease ofoperation. These recycling operations require addition of defoamer tothe fracturing fluids to decrease the foaming and ease of operation.

Alternatively, the pH of the fracturing fluid may be changed to obtaindefoaming during recycling conditions. However, this approach issusceptible to pH fluctuations and if the pH is changed back to the highfoaming state, the fracturing fluid will foam again and severely hinderthe ease of recycling operation. U.S. Patent Application No:2004/02006616 to Chatterji et al., Oct. 14, 2004, describes cationictertiary alkyl amine ethoxylates and its mixtures with anionic andamphoteric compounds which can be foamed at pH greater than 9 anddefoamed at pH less than 6 or foamed at pH less than 6 and defoamed atpH greater than 9.

U.S. Patent Application 2003/0207768 to England et. al., Nov. 6, 2003,describes a foaming well treatment fluid comprising an amphotericsurfactant. The objective of this patent is to use surfactants that havegood wetting characteristics in the presence of coal and be effectivefoaming agents. Also the recycling of the foamed fracturing fluid isobtained by lowering the pH of the fluid. However such systems aresusceptible to pH variations. In addition, adjustment of pH involvesadditional steps in the recycling operations and usually pH adjustmentinvolves addition of acids that are not desired in terms ofenvironmental acceptability.

It is desirable that the fracturing fluid does not foam in thefracturing blender or at any stage before it without the change of pHand/or addition of defoamer. Further, a foaming composition that foamsinitially but will be substantially less in foam stability after time ishighly desirable for recycling operations. Typically a foamingcomposition that will foam initially and after about 24 hours to havelow foam stability is suitable to facilitate processing.

Accordingly, there is provided a foamed fracturing fluid comprised ofwater, a self-degrading foaming composition comprising one or moresurfactant. The foamed composition will foam initially but will havereduced foam stability when the fracturing fluid is recovered duringflowback.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method offracturing a subterranean zone penetrated by a well bore comprising:

-   (a) preparing a foamed fracturing fluid comprised of water, a    self-degrading foaming composition comprising a mixture of anionic    surfactant and nonionic surfactant, and sufficient gas to form a    foam when fracturing fluid is injected; and-   (b) contacting said subterranean zone with said foamed fracturing    fluid under conditions effective to create at least one fracture    therein,    -   wherein the self-degrading foaming composition forms a        substantially less stable foam when the fracturing fluid is        recovered during recycling.

It has been unexpectedly found that the use of foaming compositioncomprising an anionic surfactant and a nonionic surfactant will foaminitially but will not foam after aging compared to the conventionalfoaming agents used in the recycle operations. The foamed fracturingfluid contains a gelling agent. This foamed fracturing fluid does notdepend on the change of pH for defoaming during recycling of thefracturing fluid.

Another object of this invention to introduce a foaming composition inthe fracturing fluid, which does not foam in the fracturing blender orany stage before it.

It is still another object of the invention to have a foamed fracturingfluid where the addition of a defoamer is not required to decrease thefoam during the recycle operations.

A further object of the invention to obtain a foaming composition and afoamed fracturing fluid independent on significantly induced pH changesby addition of acids, or buffers for defoaming during reclaim in therecycling step.

It is still another object of the present invention to have a fracturingfluid to be formulated with a relatively low level of surfactant forcost-effective performance.

DETAILED DESCRIPTION OF THE INVENTION

Surfactants in the self-degrading foaming composition in foamedfracturing fluids promote and stabilize the gas-liquid dispersions aresoap-like molecules containing a long hydrophobic paraffin chain with ahydrophilic end group. Such surfactants include anionic and nonioniccompounds. Anionic and nonionic surfactants are added in concentrationsthat range preferably from about 0.05 to about 2 percent of the liquidcomponent volume (from about 0.5 to about 20 gallons per 1000 gallons ofliquid); more preferably from about 0.05 to about 1 percent of theliquid component volume.

Anionic Surfactants

Selected anionic surfactants useful in the self-degrading foamingcomposition of the present invention include dodecylbenzenesulfonates,alpha olefin sulfonates, diphenyloxide disulfonates, alkyl naphthalenesulfonates, sulfosuccinates, sulfosuccinamates, naphthalene-formaldehydecondensates, alkyl sulfoesters and alkyl sulfoamides and mixturesthereof. Preferred anionic surfactants are sulfosuccinates andsulfosuccinamates. Most preferred anionic surfactants aresulfosuccinamates such as disodium lauramide monoethanolaminesulfosuccinamate.

Representative anionic surfactants include those of the followingstructural formulas:

and combinations thereof.

R₁ is selected from a group consisting of alkyl, aryl, alkaryl,alkylarylalkyl, arylalkyl, alkylamidoalkyl and alkylaminoalkyl; whereinthe alkyl group has about 10 to about 18 carbon atoms; wherein the arylgroup represents a phenyl, diphenyl, diphenylether, or naphthalenemoiety.

R₂ is selected from a group consisting of hydrogen, —CH₂CH₂OH, alkyl,aryl, alkaryl, alkylarylalkyl, arylalkyl, alkylamidoalkyl andalkylaminoalkyl; wherein the alkyl group has about 10 to about 18 carbonatoms; wherein the aryl group represents a phenyl, diphenyl,diphenylether, or naphthalene moiety.

“p” is 0 to about 10, preferably 0 to about 5.

M is hydrogen, an alkali metal such as sodium or potassium, or anammonium salt. M is preferably an alkali metal such as sodium orpotassium, more preferably sodium.

Nonionic Surfactants

Nonionic surfactants include but not limited to fatty acid esters,glycerol esters, ethoxylated fatty acids esters of glycol, ethoxylatedfatty acid esters of polyethylene glycol and sorbitan esters. Preferrednonionic surfactants are glycerol esters, ethoxylated fatty acids estersof glycol and ethoxylated fatty acid esters of polyethylene glycol. Mostpreferred are ethoxylated fatty acid esters of polyethylene glycol.

Selected nonionic surfactants have the structures:

R₃C(O)O—(CH₂CH₂O)_(p)—R₄

R₃C(O)OCH₂CH(OH)CH₂O—R₄

and combinations thereof.

R₃ is hydrocarbon chain containing about 10 to about 22 carbon atoms andmay be branched or straight chained and saturated or unsaturated; R₄hydrogen or a hydrocarbon chain containing about 1 to about 20 carbonatoms and may be branched or straight chained and saturated orunsaturated; “p” is from about 1 to about 20, preferably from about 5 toabout 20, more preferably from about 5 to about 12.

The water utilized for forming the foamed fracturing fluid of thisinvention can be fresh water or salt water. The term “salt water” isused herein to mean unsaturated salt solutions and saturated saltsolutions including brines and seawater. In addition water may containat least one of dissolved organic salts, organic acids, organic acidsalts and inorganic salts.

The gelling agent is added to the water for forming the water intogelled water and increasing the viscosity thereof. A variety of gellingagents can be used including natural or derivatized polysaccharideswhich are soluble, dispersible or swellable in an aqueous liquid toyield viscosity to the aqueous liquid. One group, for example, ofpolysaccharides which are suitable for use in accordance with thepresent invention includes galactomannan gums such as gum arabic, gumghatti, gum karaya, tamarind gum, tragacanth gum, guar gum, locust beamgum and the like. Modified gums such as carboxyalkyl derivatives, likecarboxymethylguar and hydroxyalkyl derivatives, like hydroxypropylguarcan also be employed. Doubly derivatized gums such ascarboxymethylhydroxypropylguar can also be used. Mixtures of thegalactomannan gums and modified gums can also be used. Optionally avariety of conventional additives can be included such as gelstabilizers, gel breakers, clay stabilizers, bactericides, fluid lossadditives and the like which do not adversely affect the self degradingfoaming tendencies of the fracturing fluid.

Foamed fracturing fluids are superior to conventional liquid fracturingfluids for problematic and water sensitive formations because foamscontain less liquid than liquid fracturing fluids and have less tendencyto leak. Also, foams have less liquid to retrieve after the fracturingoperation is complete. Moreover, the sudden expansion of the gas in thefoams when pressure in the well is relieved after the fracturingoperation is complete promotes flow of residual fracture fluid liquidback into the well. The foamed fracturing fluid can also include aproppant material for preventing formed fractures from closing. Avariety of proppant materials can be utilized including, but not limitedto, resin coated or un-coated sand, sintered bauxite, ceramic materialsand glass beads. When included, the proppant material is preferablypresent in the foamed fracturing fluid in an amount in the range of fromabout 1 to about 10 pounds of proppant material per gallon of the foamedfracturing fluid.

Examples of gases suitable for foaming the fracturing fluid of thisinvention are air, nitrogen, carbon dioxide and mixtures thereof. Thegas may be present in the fracturing fluid preferably in an amount inthe range of from about 10% to about 95% by volume of liquid, morepreferably from about 20% to about 90%, and most preferably from about20% to about 80% by volume.

The gas volumetric fraction or “foam quality” of useful foamed fracturefluids is preferably in the range of from about 50 volume percent toabout 80 volume percent gas. However, stable foams with foam qualitiesof up to about 95% can be produced. In general, the viscosity of thefoamed fluid increases with increasing quality.

The foam quality is expressed as a percentage as shown in the equationbelow:

[foam volume (ml)−liquid volume (ml)]×[100]/foam volume (ml)

Procedures for making and using foamed fracturing fluids are describedin U.S. Pat. No. 3,937,283 to Blauer et al and U.S. Pat. No. 3,980,136to Plummer et al. Briefly, these patents teach how to produce stablefoam fracturing fluids using nitrogen, water, a surfactant and a sandproppant. The foam quality ranges between 53% to 99%. The foam is pumpeddown the well and into the formation at a pressure sufficient tofracture the formation. When the fracturing operation is complete, thepressure on the well is relieved at the wellhead. The foam is carriedback into the well by the rush of expanding gas when pressure on thefoam is reduced.

U.S. Pat. No. 3,664,422 to Bullen et al., describe fracturing techniquesusing carbon dioxide as the gas phase. First, an emulsion of liquefiedcarbon dioxide and water is formed using a surfactant to promotedispersion. Proppant is added to the emulsion and the emulsion-proppantslurry is pumped down the wellbore into the formation at a pressuresufficient to fracture the subterranean formation. Downhole temperaturesare above the critical temperature of carbon dioxide so the liquidcarbon dioxide becomes a supercritical fluid as the emulsion approachesthe subterranean formation forming a stable foam.

The foamed fracturing fluid in accordance with the present invention mayoptionally contain water-soluble inorganic salt, e.g. potassium chlorideor ammonium chloride and/or at least one organic acid, water-solubleorganic acid salt or organic salt, e.g. trimethyl ammonium chloride.These salts are dissolved in water.

In an embodiment of the invention a self-degrading foaming compositionis prepared by mixing water with surfactant comprising anionicsurfactant, nonionic surfactant, and combinations thereof. The foamingcomposition may contain an organic solvent. Preferred organic solvent isisopropyl alcohol. Standard mixing procedures known in the art can beemployed since heating of the solution and special agitation conditionsare normally not necessary. Of course, if used under conditions ofextreme cold such as found in Alaska, normal heating procedures shouldbe employed.

In another embodiment of the invention the initial pH of foamedfracturing composition comprising the self-degrading foaming compositionmay be lowered or raised to decrease the initial foam quality initiallyand subsequent aging to reduce foam stability. Alternatively it may bepossible to raise the pH. The aging is done up to about 24 hours orlonger at room temperature. Further, the aging is done at elevatedtemperatures preferably from about 80° F. to about 180° F. up to about24 hours or longer.

The aging at 140° F. up to 24 hours or longer is most preferred. Theinitial decrease of pH may be by brought about by adding acid and/orbuffers. It may be possible to add a base and/or buffers to increase thepH of self-degrading foaming composition.

The following examples are presented to illustrate the preparation andproperties of foamed fracturing fluids containing self-degrading foamingcompositions and should not be construed to limit the scope of theinvention, unless otherwise expressly indicated in the appended claims.

EXAMPLES

Foamed fracturing fluids containing self-degrading foaming compositionswere prepared and were found to have reduced foam stability after 24hours of aging. These foams had good quality initially and half-life wassubstantially reduced after aging at 140° F. for 24 hours.

Materials:

-   -   Gerepon SBL-203 is an anionic surfactant, disodium lauramide        monoethanolamine sulfosuccinamate, supplied by Rhodia, Inc.

Alkamuls 600 DO is a nonionic surfactant, PEG-12 dioleate supplied byRhodia, Inc.

Example 1

A foamed fracturing fluid with a viscosity of 9-10 cP is prepared bydiluting a concentrated hydroxypropyl guar solution in tap water. About100 ml of the fracturing fluid was added to a Waring blender. Thesurfactant or surfactant blend was then added and the contents of theblender were mixed slowly. As the mixing speed was slowly increasedheight of the foam increased due to more air being trapped in the foam.The speed was gradually increased until the foam height remains stableand no further increase in the foam height was observed. The blender wasshut off, and its contents were immediately poured into a graduatedcylinder and a timer was started. The measured volume of the foam in thegraduated cylinder was the foam volume and foam quality was determinedby the following equation:

Foam quality=100×(foam volume−liquid volume)/foam volume

As time progressed, the foam separated and a clear liquid was collectedat the bottom of the cylinder. After 50% of the original liquid wascollected in the bottom of the cylinder (i.e. 50 ml) the time wasmeasured. This time was defined as the half-life. After measuring thehalf-life, the liquid was collected in a bottle and aged in an oven at aset temperature. After a given aging time at the set temperature thebottle was cooled to room temperature and quality and half-life wasmeasured.

The foam volume and time required to reach the half-life (50ml) wasmeasured, exhibiting the recyclable nature of the foamed fracturing. Thefoam testing results are shown in Table 1.

TABLE 1 Foam Testing Results Foam Volume Foam (ml) @ Half Life QualitySample ID Description Testing Conditions 75 F. (min:sec) (%) GeroponSBL-203 only R0476-70-5 0.5 ml Geropon initial 340 31:00  70.6 SBL-20324 hrs @ 140 F. 180 9:45 44.4 R0476-70-18 0.2 ml Geropon initial 30529:45  67.2 SBL-203 24 hrs @ 140 F. 185 5:45 48.6 Geropon SBL- 203 withAlkamuls 600DO R0476-70-9 0.2 ml Geropon initial 275 24:15  63.6SBL-203 + 0.05 ml Alkamuls 600 DO 24 hrs @ 140 F. 135 1:30 26.0R0476-70-10 0.2 ml Geropon initial 195 7:05 48.7 SBL-203 + 0.1 mlAlkamuls 600 DO 24 hrs @ 140 F. 125 very 20.0 fast~5 sec

Example 2

A foamed fracturing fluid of 9-10 cP was prepared as shown in Example 1.The foamed fracturing fluid containing the mixture of surfactantscompared with the control Gereopon SBL were studied at various pHvalues. The foam height, foam quality and half-life were measured atdifferent pH as well as a function of time and are shown in Table 2. Thefoam quality degraded quickly at higher pH.

TABLE 2 Effect of Initial pH on the Foam Quality and Aging Foam Final TVolume ½ pH Solution Weight Time (deg (ml) Life Quality afterDesignation Surfactant pH (g) (hr) F.) @ 75 F. (min) (%) 24 hr'sR0476-175-6 Geropon 11.8 100 0 RT 290 34.0 65.5 10.6 SBL-203 89 2 140145 3.3 38.6 (Control) 82 6 130 2.5 36.9 76 24 120 2.3 36.7 R0476-175-7R0476-85-11 11.8 100 0 RT 265 19.5 62.3 11.0 93 2 140 120 0.0 22.5 — 688 24 125 0.0 29.6 R0476-175-8 R0476-85-11 11.8 100 0 RT 260 16.5 61.511.3 98 2 135 0.5 27.4 — 6 91 24 115 0.0 20.9 R0476-175-10 Geropon 10.1100 0 RT 295 35.0 66.1 9.1 SBL-203 89 2 140 270 32.0 67.0 (Control) 82 6215 23.0 61.9 75 24 180 17.0 58.3 R0476-175-11 R0476-85-11 10.1 100 0 RT275 18.0 63.6 9.1 94 2 140 235 14.0 60.0 86 6 175 8.0 50.8 80 24 125 1.536.0 R0476-85-11: Formulated by blending 66.67% Geropon SBL-203 + 16.67%Alkamuls 600DO + 8.33% isopropanol + 8.33% Deionized water.

The invention has been described in the more limited aspects ofpreferred embodiments hereof, including numerous examples. Otherembodiments have been suggested and still others may occur to thoseskilled in the art upon a reading and understanding of thespecification. It is intended that all such embodiments be includedwithin the scope of this invention.

1. A self-degrading foaming composition comprising a mixture of anionicsurfactants selected from the group consisting ofdodecylbenzenesulfonate, alpha olefin sulfonate, diphenyloxidedisulfonate, alkyl naphthalene sulfonate, sulfosuccinate,sulfosuccinamate, naphthalene-formaldehyde condensate, alkyl sulfoester,alkyl sulfoamide, and mixtures thereof; and a nonionic surfactantselected from the group consisting of fatty acid esters, glycerolesters, ethoxylated fatty acids esters of glycol, ethoxylated fatty acidesters of polyethylene glycol and sorbitan esters; wherein theself-degrading composition has a substantially reduced foam stabilityafter aging.
 2. The composition of claim 1 wherein the anionicsurfactant is selected from the group consisting of formula (I), (II),(III), or (IV):

and combinations thereof; wherein R₁ is selected from a group consistingof alkyl, aryl, alkaryl, alkylarylalkyl, arylalkyl, alkylamidoalkyl andalkylaminoalkyl, and wherein the alkyl group has about 10 to about 18carbon atoms, the aryl group represents a phenyl, diphenyl,diphenylether, or naphthalene moiety; R₂ is selected from a groupconsisting of hydrogen, —CH₂CH₂OH, alkyl, aryl, alkaryl, alkylarylalkyl,arylalkyl, alkylamidoalkyl and alkylaminoalkyl, wherein the alkyl grouphas about 10 to about 18 carbon atoms, wherein the aryl group representsa phenyl, diphenyl, diphenylether, or naphthalene moiety; and “p” is 0to about 10, and M represents hydrogen, an alkali metal such as sodiumor potassium, or an ammonium salt.
 3. The composition of claim 1 whereinsaid fracturing fluid comprises a crosslinker.
 4. The composition ofclaim 3 wherein said crosslinker is a boron containing compound.
 5. Thecomposition of claim 3 wherein said crosslinker is selected from thegroup consisting of boric acid, borax, boron containing ores,colemanite, and ulexite.
 6. The composition of claim 1 wherein saidcrosslinker is a zirconium or titanium based metallic crosslinker. 7.The composition of claim 1 further comprising cationic surfactants,zwitterionic surfactants, amphoteric surfactants, or mixtures thereof.8. A foamed fracturing composition comprising: (a) a self-degradingfoaming composition having substantially reduced foam stability afteraging, said self-degrading foaming comprising a mixture of anionicsurfactants wherein at least one of said anionic surfactants has thegeneral formula:

wherein R₁ is selected from a group consisting of alkyl, aryl, alkaryl,alkylarylalkyl, arylalkyl, alkylamidoalkyl and alkylaminoalkyl, andwherein the alkyl group has about 10 to about 18 carbon atoms, the arylgroup represents a phenyl, diphenyl, diphenylether, or naphthalenemoiety; R₂ is selected from a group consisting of hydrogen, —CH₂CH₂OH,alkyl, aryl, alkaryl, alkylarylalkyl, arylalkyl, alkylamidoalkyl andalkylaminoalkyl, wherein the alkyl group has about 10 to about 18 carbonatoms, wherein the aryl group represents a phenyl, diphenyl,diphenylether, or naphthalene moiety; and at least one nonionicsurfactant having the general formula:R₃C(O)O—(CH₂CH₂O)_(p)R₄ wherein, R₃ is hydrocarbon chain containingabout 10 to about 22 carbon atoms, R₄ is a hydrogen or a hydrocarbonchain containing about 1 to about 20 carbon atoms; and “p” is from about1 to about 20 (b) an aqueous solution; (c) a gelling agent; and (d) agas.